In the oil and gas industry, hydrocarbon reservoirs have conventionally been accessed by vertical or near-vertical wellbores. Such reservoirs, however, are increasingly accessed via non-vertical wellbores.
Tools that have conventionally been used in the vertical or near-vertical wellbores may encounter problems when used in the non-vertical wellbores. Such tools may be lowered into wellbores as part of a tool string utilizing gravity to facilitate transport or movement therethrough. In non-vertical wellbores, gravity may be negated by frictional forces between the tool string and sidewall of the wellbore, thus resisting movement of the tool string through the wellbore. Also, particularly with open-hole wellbores not lined with casing, outer surfaces of the tool string may stick to the sidewall of the wellbore, or edges of the tool string may dig into or jam against imperfections in the sidewall of the wellbore.
Furthermore, some downhole tools achieve optimal performance when oriented in a specific direction within the wellbore. For example, certain formation testing/sampling tools achieve optimal performance when a sensor/probe of the tool faces or even contacts an intended side of the non-vertical wellbore. However, friction caused by the non-vertical nature of the wellbore trajectory impedes intended axial rotation of the tool string relative to the wellbore. Moreover, wireline, coiled tubing, and/or other means of conveying the tool string within the wellbore are often unable to facilitate rotational orientation of the tool string relative to the wellbore, such that rotation of the conveyance means at the wellsite surface is not transferred downhole and imparted to the tool string in the wellbore. Some downhole roller tools facilitate movement of the tool string along non-vertical portions of the wellbore, however, such roller tools do not axially orient the tool string within and relative to the non-vertical wellbore portions.